In photonic networks in metro access areas, network configurations are often changed due to exchanging or destination path switching of lines, such as in the add drop multiplexing (ADM) or the like, or signals. At relaying stages in the today's networks or the like, there are a lot of configurations in which signal switching are achieved by converting optical signals into electrical signals, which are subsequently converted back to optical signals.
However, from now on, in order to improve the performance desired for networks, it is expected that replacement to the dynamic optical add drop multiplexing (OADM) technique that can isolate only desired wavelengths from optical signals for increasing the speed of switching processing or cross-connect nodes that can switch input/output destination paths of un-converted optical signals on a wavelength basis.
Furthermore, in the next generation, in order to improve utilization efficiencies of lines, the processing is expected to be needed which divides optical signals into frames having a fixed length, and exchange or switch destination paths of the un-converted optical signals on a frame basis.
As a network for achieving effective operations of video distribution, data backup between data centers, grid computing, networks that carry out the above-described optical burst signal processing are promising. For achieving such networks, development of wide-scale WDM switching nodes having a high performance in terms of a response speed of optical burst switching in the order of microseconds (μs).
One example of an apparatus that carries out the above-described optical burst signal processing includes the one disclosed in, for example, Patent Reference 1. The technique disclosed in Patent Reference 1 focuses on the configuration of an optical switch apparatus that switches optical destination paths between input ends and output ends the number of which corresponds to input/output ports. For switching frame signal light that is wavelength division multiplexed (WDM) on a wavelength or frame basis, the configuration of an optical node apparatus depicted in FIG. 10 or FIG. 11, for example, is assumed.
Here, in an optical node apparatus 100 depicted in FIG. 10, wavelength division multiplexed frame signal light from a certain number (here, p that is two or more) of input transmission paths 121 is wavelength division demultiplexed at input-side wavelength mux/demux elements 101 that are formed by arrayed waveguide gratings (AWG) or the like into frame signal light for each channel and input into an N×N optical matrix switch 102. Note that the reference numeral 123 refers to WDM optical amplifiers that are inserted between the input transmission paths 121 and the input-side wavelength mux/demux elements 101.
The optical matrix switch 102 includes input ends (input ports) that receive frame signal light of each channel for wavelength division multiplexed frame signal light from the p input transmission paths 121, and includes output ends (output ports) that direct the frame signal light input from each input end to multiple (i.e., p in this example) output transmission paths 122 for each channel on a frame basis. In addition, the light output from the output ends of the optical matrix switch 102 is wavelength division multiplexed at wavelength division multiplexing portions 103 that are formed from AWGs or the like before the light is entered into the output transmission paths 122.
Here, the optical matrix switch 102 can be constructed as a deflection optical switch having a light deflection element that deflects input light upon application of a driving voltage, similar to the switch module described in the above-identified Patent Reference 1. More specifically, by driving the light deflection element with the driving voltage supplied from the driving voltage supply portion 104, the optical matrix switch 102 can form optical destination paths that are constructed from combinations of input ends and output ends. Note that another configuration of the optical matrix switch 102 includes the one disclosed in Non-Patent Reference 1.
In addition, a control information storage portion 105 stores information on the driving voltage to be provided at the above-described driving voltage supply portion 104 according to the optical destination paths to be established. A driving voltage control portion 106 outputs a control signal to the driving voltage supply portion 104 for controlling the driving voltage to be provided to the light deflection element included in the switch module 102 by looking up the contents on the control information storage portion 105 according to the optical destination paths to be established.
Note that the optical level of a respective frame for each channel that is output from the optical matrix switch 102 to each output transmission path 122 is equalizised by means of the variable attenuation (VOA) adjustment of the above-described driving voltage in the optical matrix switch 102. The information on the driving voltage for the variable attenuation control is stored in the control information storage portion 105.
More specifically, the level of frame signal light of each channel that is wavelength division demultiplexed at the input-side wavelength mux/demux elements 101 is monitored by the input signal light monitors 111 formed by photo diodes via photo couplers 118. A target attenuation additional amount is derived at the driving voltage control portion 106 by subtracting the inherent loss at the optical matrix switch 102 and the wavelength division multiplexing portion 103 from the monitor result. The driving voltage information for achieving the target attenuation additional amount value is obtained from the control information storage portion 105, and provided to the driving voltage supply portion 104 as a control signal. Thereby, equalization of the level of the light that is undergone the destination path switching processing and is output from each output end is achieved.
Note that reference numeral 110 refers to a wavelength converting portion that carries out a predetermined wavelength conversion on particular frame signal light that is to be input into the optical matrix switch 102 requiring wavelength conversion. For this purpose, the optical matrix switch 102 includes output ends for setting routes via the wavelength converting portion 102, and input ends for receiving frame signal light again into the optical matrix switch 102, wherein the light is underdone wavelength conversion processing to direct to the output transmission paths 122 for destination path switching.
Accordingly, assuming that the number of the both input ends and the output ends coupled to the above-described wavelength converting portion 110 is m, the numbers of the input/output transmission path 121 and 122 are p. Assuming that the number of the maximum channel that can be accommodated for wavelength division multiplexing at each of the input/output transmission path 121 and 122 (i.e., the number of light to be wavelength division demultiplexed at the input-side wavelength mux/demux element) is n, the number N of the input/output ends of the optical matrix switch 102 can be expressed as N=n×p+m.
In addition, an update control portion 109 is configured to store and manage, in the control information storage portion 105, driving voltage information that is used for coupling an input end and an output end for expected destination path switching before operation of the apparatus is initiated and driving voltage information for the variable attenuation control. The update control portion 109 is appropriately configured to update and control driving voltage information for optical destination paths that are actually operated but setting of destination paths are waited, and driving voltage information for variable attenuation control.
For this purpose, the optical node apparatus 100 depicted in FIG. 10 is configured to monitor the level of input/output light of reference light at optical destination paths that are not operated or are waiting to be operated between input/output ends of the optical matrix switch 102. The update control portion 109 is configured to update and control driving voltage information stored in the control information storage portion 105 by monitoring the input/output level of the reference light to the optical destination path.
Here, as a configuration for monitor the input/output level of the above-described reference light, provided are: a light source 112, for example, in the L (Long) band that is different from the C (conventional) band used as the wavelength band wavelength band of the frame signal light; an input reference optical monitor 113 that monitors the level of the L-band light output from the light source 112 as an input reference light level; a 1×N coupler 114 for dividing the light from the light source 112 into N reference light; a C/L separation coupler 115 for bundling each reference light divided by the 1×N coupler 114 into respective N input ends included in the optical matrix switch 102; respective C/L separation couplers 116 for extracting the above-described reference light on light propagation path for propagating each frame signal light output from each of the N output ends; and an output reference optical monitor 117 that monitors each output reference light in the L-band from the C/L separation couplers 116.
Thereby, the update control portion 109 directs the reference light from the light source 112 to the optical destination path to be updated at the optical matrix switch 102, and updates and controls the driving voltage information stored in the control information storage portion 105 based on the monitor result from the above-described input reference optical monitor 113 and the output reference optical monitor 117.
An optical node apparatus 130 depicted in FIG. 11 is different from the optical node apparatus 100 depicted in FIG. 10, and includes a light source 112A that outputs light in the wavelength band substantially the same as that of frame signal light (C-band). The reference light from the light source 112A is propagated through optical circulators 119a and 119b provided on both of the output end side and the input end side of the optical matrix switch 102, from the output ends of the optical matrix switch 102 towards the input ends (i.e., at the direction opposite to the propagation direction of the frame signal light). In this case, similar to the case in the optical node apparatus 100 depicted in FIG. 10, the update control portion 109 may update and control the contents in the control information storage portion 105 based on the monitor result from the input reference optical monitor 113 and the output reference optical monitor 117.
In addition to the above-cited techniques, Patent Reference 2 discloses a technique related to the present invention:    Patent Reference 1: Japanese Laid-open Patent Publication No. 2006-287453    Patent Reference 2: Japanese Laid-open Patent Publication No. 2000-358261    Non-Patent Reference 1: Y. Kai et al., “4×4 high-speed switching subsystem with VOA (<10 μs) using PLZT beam deflector for optical burst switching”, Optical Society of America, OFJ7, 2006
However, for optical burst switching frame signal light of the WDM in the manner described above, the input reference optical monitor 113 and the output reference optical monitor 117 are required for each of the input ends and the output ends included in the optical matrix switch 102 for propagating respective reference light, as depicted in FIG. 10 and FIG. 11, as well as the C/L separation coupler 115 and 116 the optical circulators 119a and 119b. Accordingly, since a large number of optical devices are required for propagating reference light on the optical destination paths in the optical matrix switch 102, which may incur increase in the manufacturing cost of the apparatus and complexity of optical wiring.
Neither the above-described Patent References 1 nor 2 provides any structure for simplifying the optical wiring in an optical node apparatus for optical burst switching of frame signal light of the WDM.